The present invention relates generally to the control of the direction and speed of a locomotive which bears on the ground, on the one hand, with a bogie formed by at least two independent driving rollers or bogie members and, on the other hand, with a support assembly, if necessary reduced to a single steerable support member.
The invention concerns in particular, but not necessarily exclusively, compacting locomotives with hydrostatic transmission, for example compacting locomotives whose roller members constitute the vibrating elements and each of which is individually rotated by a respective independent hydraulic motor, such as are described in particular in French Pat. No. 1,573,169, and also in French Pat. filed under No. 7507655 and published under No. 2,323,543.
One of the problems to be overcome in the construction of locomotives of this type is to ensure complete independence between the speed control and the directional control, whatever steering angle is applied to the support member. In French Pat. No. 1,573,169 there is described a mechanical solution to this problem when the support member is a simple guide such as a freely rotating roller. In French Pat. No. 75,076,55 this mechanical solution is extended to the case in which the roller constituting the support not only guides but also drives. This mechanical solution has given and still gives satisfaction, but has disadvantages which are as follows.
First, the independence of the speed control of the locomotive with respect to its directional control is only brought about to the extent that in a bend the speed of rotation of that driving member situated outermost in this bend remains below a maximum speed value corresponding to the maximum output from the pump supplying the motor which controls it: above this maximum speed value the speed of rotation of that driving roller situated innermost in the bend decreases rapidly, in such a way that the direction followed by the locomotive, which direction is imposed by the relative speeds of rotation of the driving roller members of this latter, remains consistent with the steering angle applied, moreover, to the ground support of this locomotive.
As the speed of rotation of the inner driving roller situated innermost thus decreases, whereas that of the outer driving roller reaches its maximum value, the mean speed of forward movement of the locomotive decreases automatically, which in practice results in an automatic return of the speed-control lever of this locomotive.
When the locomotive returns to a straight line, this lever is thus no longer in its original position and the initially set speed of forward movement prevails no longer, it being necessary for the driver of the machine to operate this speed-control lever once more so as to regain this initial rate of forward movement.
Furthermore, the mechanical solution described in the aforementioned French patents essentially does not make it possible to obtain different directions of rotation at the two driving roller members and thus limits the steering angle which can be imparted to the steerable support.